Groundwater Recharge
water used, saving approximately USD 390,000 a This historical system was neglected after the introduction
year. In China’s Gansu Province, the annual precipitation of a piped water system to the Kathmandu Valley about
of 300 mm caters to 2 million people and supplies a century ago. The stone spouts have been further
supplementary irrigation for 236,400 hectares of land. affected by the recent uncontrolled exploitation of
In India, direct recharge of rainwater into the ground groundwater and the destruction of the former rainwater
(Mahnot et al. 2003) resulted in groundwater level collection ponds and recharge areas. A recent study
increases of up to 5 to 10 metres in just two years. found that about 400 stone spouts and several hundred
traditional dug wells in the Kathmandu Valley are now
Given such successes around the world, it is clear that
dry (NGOFUWS 2006).
rainwater harvesting has great potential to address some
of today’s water crises in many of the world’s urban areas.
Water demand and exploitation of groundwater
in the Kathmandu Valley
Kathmandu Valley has been suffering from a shortage
of drinking water since the 1980s, and the situation
is getting worse. The Valley’s current water demand
is about 280 million litres per day (MLD), but the
Kathmandu Valley Water Utility (KUKL) can only supply
about 86 MLD during the dry season and 105 MLD
during the wet season. To meet the supply-demand gap,
groundwater from both shallow and deep aquifers (more
than 200 metres) is being heavily extracted by small- to
large-scale users, including KUKL itself. This unregulated
extraction is depleting the aquifers; especially the
deep aquifers are not easily rechargeable due to the
Valley’s impermeable black clay (JICA 1990). The
overall groundwater extraction rate exceeds the natural
Figure 1: Schematic diagram of traditional water supply system
(CIUD/UN-HABITAT 2009)
recharge capacity by 6 times, resulting in a lowering of
the groundwater table by approximately 2.5 metres per
Rainwater harvesting potential
year (MPPW 2002). An immediate consequence of the
depletion of shallow groundwater aquifers is that dug
Rainwater harvesting and artifi cial recharge into shallow
wells, hand pumps, and traditional stone spouts can no
and deep aquifers offers a promising approach for
longer provide water as they once did. The groundwater
reversing the trend of water resource exploitation and
quality is also a concern, chemical pollutants such as
groundwater depletion. The average rainfall in the
arsenic, ammonia, and nitrate have been detected in
Kathmandu Valley is around 1900 mm: more than twice
deep aquifers in many areas of the Valley.
the world average. Approximately 1.2 billion cu.m/year
or 3353 million litres per day (MLD) of rainwater falls in
Historical water management
the 640 sq.km Valley. This is about 12 times the present
water demand.
The historical cities in the Kathmandu Valley were
established over 2000 years ago. The Kirat regime
The author has been collecting rainfall data at one
constructed rainfed ponds and springs. Later, the
location in Kathmandu since January 2005. The
Lichhavi kings linked the ponds to stone spouts and
average annual rainfall in this location over the last four
dug wells to provide water to the cities. These structures
years was about 2500 mm, higher than the estimated
were expanded during the Malla regime, when
valley average. About 80% of total rainfall on a building
elaborated networks of canals, ponds, and water
can be collected easily (UN-HABITAT 2006), thus in
conduits were constructed (Figure 1). This water supply
theory a building with a roof area of 100 sq.m could
and management system supplied adequate good
collect up to 200 cu.m of rainwater per year, adequate
quality water to the urban population throughout the
for a family of fi ve with a water demand of about 170
year. Guthis (local community groups) were formed to
cu.m per year. But it is not practical to store all this
maintain the overall supply system. Once a year, on the
water, thus artifi cial groundwater recharge to replenish
Sithi Nakha festival, the guthis worked together to clean
the aquifers is likely to be one of the best options for the
up the ponds, wells, and water canals.
28
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